The present invention relates generally to the art of electric motors and other electromechanical machines. More particularly, the invention relates to an electric motor including a novel structure to achieve electrostatic shielding.
The shaft of an AC induction motor or other electromechanical machine is often supported by bearing assemblies maintained in position by the machine housing. In one known construction, each bearing assembly is supported by a portion of the housing known as the "end bell." As its name implies, the end bell is located at one axial end of the housing, and defines a hole through which the rotatable shaft freely extends.
During operation of an electric motor, capacitive coupling can often occur between the stator and rotor. Occasionally, the potential difference developed in this manner will exceed a magnitude necessary to break down insulating grease in the bearing assembly. In this case, currents may arc or discharge from the bearing balls or rollers to the outer bearing race causing "pits" or other undesirable effects. As a result, more frequent servicing of the bearing assemblies may be required.
The prior art has provided electrostatic shield arrangements to reduce capacitive coupling between the rotor and stator, and consequent current discharge through the bearing assemblies. Examples of various shield configurations can be seen in U.S. Pat. No. 5,661,353 to Erdman et al., incorporated herein by reference. While these arrangements have been effective at reducing capacitive coupling, a further need exists for various novel electrostatic shield structures that may be advantageous in particular applications.